DNA polymerase ζ generates tandem mutations in immunoglobulin variable regions

• DOI: 10.1084/jem.20112234
• Publication Date: 2012-05-22T02:51:23Z
• Authors: Huseyin Saribasak; Robert W. Maul; Zheng Cao; William W. Yang; Dominik Schenten; Sven Kracker; Patricia J. Gearhart
• Keywords: 0301 basic medicine; Heterozygote; 0303 health sciences; Brief Definitive Report; Immunoglobulin Variable Region; DNA-Directed DNA Polymerase; DNA Mismatch Repair; Mice, Mutant Strains; 3. Good health; DNA-Binding Proteins; Mice; 03 medical and health sciences; MutS Homolog 2 Protein; Mutation; Animals; Somatic Hypermutation, Immunoglobulin; Uracil-DNA Glycosidase; Cell Division

Low-fidelity DNA polymerases introduce nucleotide substitutions in immunoglobulin variable regions during somatic hypermutation. Although DNA polymerase (pol) η is the major low-fidelity polymerase, other DNA polymerases may also contribute. Existing data are contradictory as to whether pol ζ is involved. We reasoned that the presence of pol η may mask the contribution of pol ζ, and therefore we generated mice deficient for pol η and heterozygous for pol ζ. The frequency and spectra of hypermutation was unaltered between Polζ+/− Polη−/− and Polζ+/+ Polη−/− clones. However, there was a decrease in tandem double-base substitutions in Polζ+/− Polη−/− cells compared with Polζ+/+ Polη−/− cells, suggesting that pol ζ generates tandem mutations. Contiguous mutations are consistent with the biochemical property of pol ζ to extend a mismatch with a second mutation. The presence of this unique signature implies that pol ζ contributes to mutational synthesis in vivo. Additionally, data on tandem mutations from wild type, Polζ+/−, Polζ−/−, Ung−/−, Msh2−/−, Msh6−/−, and Ung−/− Msh2−/− clones suggest that pol ζ may function in the MSH2–MSH6 pathway.